The Dreaded NO SPARK Issues - Ready to Scream!

[onthesolidrock]

We bought a 1983 Porsche 944 that; according to the previous owner, ran until he parked it for the winter.

The car does not have any spark to the distributor. We have through the posts here and have read the instructions on Clarks garage and we are still not getting spark.

We have:

Replaced the coil
Replaced both speed / position sensors
Replaced the DME relay
Replaced the DME unit
Checked all fuses

We have fuel pressure to the fuel rail

We have 12 volts to the + side of the coil, but nothing is getting to the distributor.

Please, if you have ANY ideas, even if they sound strange, please, please, please, do share!

[John_AZ]

I reread the old posts.

DO you have the " 1/16" Tach needle Bounce" when initial cranking?
Are the new sensors set at proper gap?



The AFM connection, nothing will start unless the AFM is plugged in. Search for AFM info.

Are the plug wires in the correct position on the distributer?

The DME spare unit---are you sure it is good? (not the DME relay).

Have you done the test on

Have you cleaned All the ground points?



The "football" ground under the dash drivers side-----above the fuse panel needs to be cleaned.

Clean all contact surfaces on the relays and fuses.

Did you do the sensor check from ecudoctors?
How to test a Porsche 944 RPM and TDC sensor

Just a start.

J_AZ

[onthesolidrock]

Thanks for the pointers,

We just got a used / tested DME which has a 30 day gaurantee. We really don't know how to test one of these ourselves.

We do not have tach bounce.

We have not been able to find a proper testing meter for the fuel rail; however we do have fuel there, as it will spray out if we loosen the flare nut.

I crawled under the car and put my hand on the fuel pump. When the ignition key is turned to the "on" position, nothing happens, when we roll the engine over, I can feel the pump kick on for a bit. Most cars will have the fuel pump kick on when the key is at the "on" position.

Your thoughts on this?

We will go over these ground points and see what happens.n

I will search out what the AMF is, as that is a new term to us.

Thanks

[Bradical]

The DME relay is going to energize the fuel pump when the ignition is on. However, with no tach bounce...

Did you verify the speed/reference sensors are not switched at the plug connectors? Try swapping them and see if you get tach bounce if you haven't already.

[John_AZ]

Originally Posted by onthesolidrock

Thanks for the pointers,

We just got a used / tested DME which has a 30 day gaurantee. We really don't know how to test one of these ourselves.

We do not have tach bounce.

Your thoughts on this?
Thanks

To see if the DME is sending a signal to the reference sensors, do the test:
How to test a Porsche 944 RPM and TDC sensor

J_AZ

[wildcat077]

I had an issue with my race car where it wouldn't start sometimes and it was one of the connectors for the reference sensors on the engine harness end ...
One of the connectors is made of two wires while the other is one wire and some twisted shielding foil,that is the one that was giving the no start issues.It would eventually start after wiggling the connector around but i ended up splicing in a new connector,although it was a pain to do it correctly,it solved my no start problem !

Worth taking a look,just peel back the rubber boot on the engine side connectors and have a peak ...

Cheers
Phil

[DannoXYZ]

Did you space the sensors away from the flywheel-teeth optimally? That affects the signals and many people have replaced DME, speed/ref-sensors, spark-plugs & wires, injectors, injector-harnesses, ignition-coils, distributor, cap/rotor, timing-belt, etc. Pretty much ALL of the electronic parts. Only to find at the end that their perfectly-good old speed/ref-sensors were just incorrectly spaced.

I don't even bother with voltmeter tests and jump straight to the 'scope. You should get a waveform like this:


1. the ref-signal should be at least 2v and start on a rising slope
2. the speed-signal shoulc be at least 2.5v peak-to-peak

If the sensors are spaced too far away from the flywheel, the voltages will be too low for the DME to register.

Some things to check:

- swap the sensor-connectors, sometimes they get swapped with replacement
- check for +12v at one of the coil-terminals
- check for +12v on one side of all the injector connectors (wires are crispy, be very, very careful and don't yank on them).

[kdjones2000]

Have you checked your rotor and distributor?

[MrAlien]

I have had those connectors on the speed and reference sensor fall apart, also seen the wiring for the reference sensor go bad on one car. you can test the resistance at the pug for the dme to see if the wiring and connectors are good.